BETA-ENDORPHIN INHIBITION OF PROGESTERONE SECRETION BY PORCINE GRANULOSA-CELLS DURING FOLLICLE DEVELOPMENT

Exogenous beta-endorphin or the opioid antagonist, naloxone, was added to the culture medium of control or LH-treated granulosa cells to elu cidate the role of beta-endorphin in follicular steroidogenesis. beta- endorphin decreased basal progesterone (P-4) production by Gc isolated from small and medium follicles and had no effect on P-4 production b y cells from large follicles. beta-endorphin decreased P-4 production by LH-treated Gc isolated from small, medium and large follicles. Nalo xone increased basal P-4 production by cells from small and medium fol licles and had no effect on P-4 production by Gc from large follicles. Neither agent had any effect on basal oestradiol (E-2) secretion by G c from any of the follicles. However, E-2 secretion by LH treated Gc f rom all sizes of follicles was inhibited by beta-endorphin, with the g reatest effect on cells from small follicles. We conclude that opioid peptides act in the follicle in a paracrine manner to prevent excessiv e basal progesterone secretion by Gc and may also be involved in the r egulation of LH action on granulosa cells steroidogenesis during folli cle development. (C) Inra/Elsevier, Paris.